FWIW I was talking about this with a Japanese Lady who trained for years with Tohei in Japan before moving here. She noticed I was wearing one of my knee braces (muscles get out of balance then my kneecap likes to dislocate and things go from bad to worse). I asked her if Tohei ever talked about whether to move from the balls of the feet or the heels. She told me that it didn't matter which as long as things were moving together. In other words, you don't let any part of the body "drive" any other part. I think this goes to Kevin's comment about torsional stresses on knees, etc. She said a body with "ki flowing" will move naturally and smoothly, all connected, all working together to create movement. No one part makes other parts move. So my take away from that comment was to be connected up correctly and to allow every part of the "chain" to work together in movement rather than being the usually stiff-hipped guy I normally am. That's what I fight. Sink a bit more, get the hips moving, then things start to loosen up all over the place. Then I can move and turn from the balls of the feet, or the heels, just depending on which works better for what I'm doing. Which is now sounding exactly like what has already been said...